package one;

public class AppConfig {
        private  static AppConfig instance;

    private AppConfig(){
        System.out.println("AppConfig 懒汉式 初始化... ...");
    }
    public static AppConfig getInstance() {
        if(instance == null) {
            synchronized (AppConfig.class) {
                if(instance == null) {
                    instance = new AppConfig();
                }
            }
        }
        return instance;
    }
}
